mjhjmtu

I'm working on a script and I need to build the tar command dynamically.

Here are two examples to illustrate what I'm trying to do :

#!/bin/bash

TAR_ME="/tmp"

EXCLUDE=("/tmp/hello hello" "/tmp/systemd*" "/tmp/Temp*")
_tar="tar "`printf -- '--exclude="%s" ' "$EXCLUDE[@]"`" -zcf tmp.tar.gz"
echo COMMAND: "$_tar"
$_tar "$TAR_ME"

echo -e "nnNEXT:nn"

EXCLUDE=("--exclude=/tmp/hello hello" "--exclude=/tmp/systemd*" "--exclude=/tmp/Temp*")
_tar="tar "`printf -- '%s ' "$EXCLUDE[@]"`" -zcf test.tar.gz"
echo COMMAND: "$_tar"
$_tar "$TAR_ME"

I want to be able to use _tar as a command, I've been able to make it work with classic path, but I need it to work with spaces in folders' name.
And every single time I got errors that look like :

COMMAND: tar --exclude="/tmp/hello hello" --exclude="/tmp/systemd*" --exclude="/tmp/Temp*" -zcf tmp.tar.gz /tmp
tar: hello": Cannot stat: No such file or directory

COMMAND: tar --exclude=/tmp/hello hello --exclude=/tmp/systemd* --exclude=/tmp/Temp* -zcf test.tar.gz 
tar: hello: Cannot stat: No such file or directory

Just one thing you need to know, I need my script to work on very old machines, meaning I can't use last bash features.

Don't try to make an executable string. Instead build the arguments in an array and use that when calling tar (you are already using an array properly for EXCLUDE):

#!/bin/bash

directory=/tmp

exclude=( "/tmp/hello hello" "/tmp/systemd*" "/tmp/Temp*" )

# Now build the list of "--exclude" options from the exclude array:
for elem in "$exclude[@]"; do
 exclude_opts+=( --exclude="$elem" )
done

# Run tar
tar -cz -f tmp.tar.gz "$exclude_opts[@]" "$directory"

With /bin/sh:

#!/bin/sh

directory=/tmp

set -- "/tmp/hello hello" "/tmp/systemd*" "/tmp/Temp*"

# Now build the list of "--exclude" options from the $@ array:
for elem do
 shift
 set -- "$@" --exclude="$elem"
done

# Run tar
tar -cz -f tmp.tar.gz "$@" "$directory"

Note the quoting of $@ in the sh code and of both $exclude[@] and $exclude_opts[@] in the bash code. This ensures that the lists are expanded to individually quoted elements.

Related:

• How can we run a command stored in a variable?

mix()
 p=$1; shift; q=$1; shift; c=
 i=1; for a; do c="$c $q "$$i""; i=$((i+1)); done
 eval "$p%%*$c$p#*%"

mix 'tar % -zcf tmp.tar.gz' --exclude "/tmp/hello hello" "/tmp/systemd*" "/tmp/Temp*"

EXCLUDE=("/tmp/hello hello" "/tmp/systemd*" "/tmp/Temp*")
mix 'tar % -zcf tmp.tar.gz' --exclude "$EXCLUDE[@]"

Extending the answer here.
This doesn't rely on any bashisms, it will also work fine with debian's /bin/sh, and with busybox.